This invention relates generally to electrically controlled unit injectors. Sisson et al in U.S. Pat. No. 4,281,792 illustrates an electrically controlled unit injector capable of controlling the timing and metering functions by a single solenoid. This injector may be characterized as having four modes of operation. A preinjection timing mode, an injection mode, a fuel dumping mode and a metering mode. This type of unit injector utilizes a cam driven pumping piston or plunger and a floating or metering plunger both situated within a bore. The metering piston is hydraulically coupled to the pumping plunger. The volume of the bore between the two plungers defines a variable volume timing chamber and the volume below the metering plunger defines a metering chamber. Fuel is received into the timing chamber under the control of a solenoid valve. Sisson et al illustrates the use of a two-way valve with fuel input to the metering chamber directly from the fuel supply. Other embodiments have shown the utilization of a three-way valve which selectively controls the flow of fuel from the supply to either the timing and metering chambers. During the pre-injection timing phase of operation, the timing valve is maintained in a condition to permit the pumping piston to force fuel out of the timing chamber, through the control valve and back to supply. Fuel injection systems often utilize a plurality of similar injectors connected to a common fuel supply, the pumping of the fuel from the timing chamber of each unit injector may cause pressure and flow variations to occur within the supply line, thus degrading the fuel injection accuracy of the remaining injectors.
The present invention is directed to a means for eliminating supply pressure dynamics generated by a fuel pulse which is created by pumping the timing chamber fuel back into the supply line during the pre-injection timing mode of operation.
Accordingly, the present invention comprises in combination: an injector having the self-actuating three-way valve lodged in a passage between the fuel injector supply inlet and the control valve. This three-way valve permits fuel to flow from supply through to the electronic control valve during the metering mode of operation while prohibiting fuel to be dumped on to the supply line during the pre-injection timing phase of operation.